1. Field of the Invention
The present invention relates generally to a mobile communication system supporting voice and data services, and in particular, to a method and apparatus for efficiently transmitting information about the status of a forward channel from a mobile station (MS) in a multi-carrier mobile communication system.
2. Description of the Related Art
A typical mobile communication system such as CDMA (Code Division Multiple Access) provides only a voice service. However, growing user demand and development of mobile communication technology have led to mobile communication systems that additionally provide a data service. One of them is a so-called 1xEV-DV (Evolution-Data and Voice) system.
In the 1xEV-DV mobile communication system, a plurality of MSs report to a base station (BS) measurements of the status of a forward channel from the BS by R-CQICHs (Reverse-Channel Quality Indicator Channels) and the BS then determines an MS to receive forward packet data and its related transmission parameters based on the forward channel status measurements. Here, the forward channel status is measured as the carrier-to-interference ratio (C/I) of a forward pilot channel from the BS.
FIG. 1 is a block diagram of an R-CQICH transmitter in a typical 1xEV-DV mobile communication system. Referring to FIG. 1, a C/I measurer 101 measures the C/I of a forward pilot channel signal and a C/I information generator 102 generates C/I information in a predetermined number of bits by quantizing the C/I measurement. Mapping of C/I measurements to C/I information is illustrated in Table 1 below.
TABLE 1C/I informationC/I measurement of forward pilot(a4, a3, a2, a1, a0)NULL (below −14.5 dB or MS not ready)00000−14.5 to −13.1dB00001−13.1 to −11.6dB00010−11.6 to −10.2dB00011−10.2 to −8.8dB00100−8.8 to −7.4dB00101−7.4 to −5.9dB00110−5.9 to −4.5dB00111−4.5 to −3.1dB01000−3.1 to −1.6dB01001−1.6 to −0.2dB01010−0.2 to 1.2dB010111.2 to 2.6dB011002.6 to 4.1dB011014.1 to 5.5dB01110Above 5.5dB01111
In Table 1, one bit in the position of a4 is reserved. Therefore, the C/I information is represented actually in 4 bits.
A block encoder 103 encodes the C/I information at a coding rate of (12, 5). A Walsh coverer 104 covers the 12 code symbols received from the block encoder 103 with a Walsh code of length 8. The Walsh code is determined according to a 3-bit best sector indicator (BSI). The BSI indicates a BS (i.e. sector) in the best forward channel status in an active set listing BSs (sectors in a sectored BS) communicating with an MS.
A Walsh spreader 105 spreads the 96-bit Walsh covered sequence received from the Walsh coverer 104 with a Walsh code assigned to an R-CQICH and transmits the spread signal to the BS.
The 4-bit C/I information and the one reserved bit are transmitted in every reverse channel slot of 1.25 ms. The C/I information is equivalent to 3200 bps and each MS that is to receive a packet data service transmits C/I information to the BS. This C/I information transmission uses a large amount of reverse transmission capacity that might otherwise be used for transmission of traffic data.
Moreover, the R-CQICH configuration is applicable only up to a 2xEV-DV system using a single carrier. An advanced 3xEV-DV system uses multiple carriers to increase system efficiency and the multiple carriers are in different forward channel statuses. Therefore, there is a need for a preferable method of transmitting forward channel status information in a multi-carrier mobile communication system.